A new study by Arlington County Commuter Services (ACCS) examines the travel and parking behaviors of residents by looking at a sample of residential site plan buildings.

Site plan buildings are those that require special approval from the County Board in order to be developed because they need some kind of exception to the zoning ordinance (such as more units, more floor area, or fewer parking spaces). Consistent with the concept of “special exception” projects, both staff and community members have opportunities for input before the approval, and each approval raises questions about the impacts of the development into the future.

The new study begins to speak to some of the big picture questions as they relate to transportation, such as “are we still moving more people without more traffic?” and “are we parking these buildings at the right level?”

One of the more intriguing results of the study: Most parking garages neither filled nor emptied over the course of a week. Most fluctuated between 20 and 80 percent full. Several garages never dropped below 40 percent full. The maximum occupancy suggests parking supply may be too high, while the minimum occupancy, particularly in Metrorail corridors, suggests that many cars in these Arlington residential buildings are not used for commuting, and in fact may be rarely used at all.

The fact that garages are not being filled would suggest a tendency to overestimate the number of needed parking-garage spaces in Arlington’s site-planned buildings, both by the County Board granting the building permits, and by developers and consumers who may favor access to parking but then fail to use the spaces. The high minimum occupancies measured, coupled with lower-than anticipated trip-generation rates across all study sites, suggest that even when households own cars, they are not necessarily using them as much as anticipated.

The ACCS study results are an opportunity to influence policy makers involved in the county’s site-plan review process to push for a reduction of parking spaces, particularly in buildings located in the county’s Metrorail corridors. Properties developed “by-right” were not included in this sample, but since by-right parking ratios are higher than site plan approved ratios, it may be that those properties provide too much parking as well.

The ACCS research program is now underway with a similar study of commercial properties. Information on occupancy and trip generation of commercial and shared-use parking garages will provide a useful counterpoint to the residential results, informing and supporting the ongoing development of Arlington’s mixed-use urban villages.

As policy for the future is shaped, another consideration for residential buildings with a lifespan of decades is flexible provision for the transportation behavior of the future. There is considerable work underway worldwide that is likely to make cars smaller, safer, cleaner, more efficient, and less expensive. Ten years from now and beyond, consumers may embrace such vehicles, even if they don’t use them every day.

Or there may be a trend toward fewer personal vehicles. Some forecasts hold out the prospect that car-sharing will be much more widespread, and that privately-owned vehicles won’t be so popular.

Another consideration is that newer versions of future cars may be parked via remote control with nobody in them, so parking spaces with no room for the passenger doors to open may be possible…higher density parking via precise robotic maneuvering.

CATES in Seattle is assessing these possibilities now with support from the Graham Environmental Sustainability Institute and the Connected Vehicle Proving Center at the University of Michigan.

Looking at the study data out of context will and is providing false results. In my personal experience with the parking garage I use, currently the garage is never full, yet just a few years ago before the economy slowed down (a lot) the garage was FULL to capacity every weekday. During the recent boom years, the streets around Ballston were VERY FULL of people walking about the area, but today the number of people on the street pales in comparison. Using current statistics, if reductions are made today in the number of parking spaces required, then tomorrow when the economy greatly recovers, we will have a large shortage of parking.

Planners (myself included) love to bemoan our society’s over-reliance on the automobile.
We attribute it to misguided-land use policies that promote sprawl, and funding biases that

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Arlington County Commuter Services (ACCS) is funded in part by grants from the U.S. Department of Transportation (DOT), the Virginia Department of Transportation (VDOT) and the Virginia Department of Rail and Public Transportation (DRPT).

Mobility Lab is a research-and-development initiative for "transportation demand management - moving people instead of cars." Based in Arlington, Virginia - which has one of the largest transportation-demand-management programs in the U.S. and removes 45,000 car trips from the county's roads each work day - Mobility Lab seeks solutions, stories, and partnerships from all over the world.